Should range hood exhaust go horizontal or up then out?

2 months ago

I have my gas range on an exterior wall (these exterior walls are 100+ year old and solid brick) and need to decide on a range hood, something the 400-600 max cfm category. A vent will be cut in the brick as there is no useable vent right now.

I can get some range hoods that vent straight back, horizontal exhaust. It seems more standard that hoods vent up, though. the ceiling is 9.5' tall, so i could vent upwards about 3-4' before a 90 degree bend and then go horizontal outside. There is no way to go straight up to the roof, it has to vent to the wall.

so my question is, is one of these exhaust paths preferred? And if I go horizontal, am I locking myself into a non-standard exhaust type that might make it difficult to replace the hood in the future?

Putting out the bat signal for @kaseki I have read so many of your posts but not quite sure about this.

Drawing (not to scale)

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Comments (4)

Lisa Leone
Original Author
2 months ago
The problem is there's no ductwork or space for ductwork anywhere in the house. The space directly above this is a bedroom and not a great place for a duct or chase. The current vent has 2 90 degree turns and goes directly out a window so anything is pretty much an improvement.

I am leaning towards up and out sideways for the noise reasons, but didnt know if the efficiency or direct horizontal is better? the space between the windows is a little over 6' so the spacing is not a big issue.
kaseki
2 months ago
While the longer path with the 90 elbow will have higher pressure loss than directly out the back, this can be compensated by blower selection. Baffle pressure loss and insufficient MUA can dominate the elbow loss. The up path does provide a potential for adding a silencer into the path if you have 3 to 4 ft of rise and a free diameter about 4 inches greater than that of the duct. For external blower only. If used, a chimney cover will have to be larger.

For either path you can put a down-roof type external blower and its housing on the side of the house, or use an internal hood blower.

What is your basis for your intended CFM values, and are they actual or blower rated CFM?
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I have checked with my insurance company. They don't care if I put a commercial, non-residential range in my kitchen. I'd notify them in writing before proceeding, of course. Weight should not be an issue. 36-inch to 48-inch ranges weigh from 600 to 800 pounds, which is about five people. The basement is unfinished, so if I measure any deflection I can sister the joists or even add a post. I've talked to a local restaurant supply store. They are happy to sell me a used range. For a new range, they want to sell to a business, which I can do. They will only deliver to my front door, will not install, and the range will have no warranty - all perfectly understandable. The applicable building code has no provision for commercial appliances in residential dwellings. Then again, I've never pulled a building permit just to buy a new kitchen appliance. Interestingly, the code says nothing meaningful about makeup air or required CFMs in residential kitchens - I will look again, though. Visually - hmm. I did a quick sketch - maybe I can make this look palatable, maybe not. So, this brings me to the original issue, which is function and safety. I have friends with commercial ranges in their home kitchens. These ranges don't set the kitchen ablaze, nor do they turn the kitchen into a sauna, nor do they brand you like a calf if you brush up against them. They are not ''on'' at full-bore 12 hours/day, jammed in a room with more ranges, broilers, griddles, ovens, fryers, all working non-stop. I believe that, if properly installed with appropriate clearance to combustibles and appropriate venting and professionally installed gas connections, a commercial range is just as safe as any range. When I add the fire suppression and gas shut-off, I think it'll be safer. But I do need to get the venting right. This house is leaky, but hopefully as we work on it, it'll get tighter, and I don't want any backdrafting. The way I see it, the exhaust and makeup issues I'm wondering about are not unique to commercial ranges. Someone planning a 60-inch "professional" range with char-broiler would face the same issues. I know that discussions about commercial appliances on GW tend to elicit cautionary responses, which I understand and appreciate. But, for the purposes of planning HVAC, let's forget the "commercial" aspect. Let's pretend I'm planning a 60-inch Bluestar and for some reason I like to cook with burners on high and the oven door ajar and the char-broiler blazing.
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As I read your situation you'd have the xost going up then making a 180ÃÂº down under then probly another 90ÃÂº to horizontal.Something like that anyway. Be sure to size the duct diameter accordingly because each bend will be equivalent to several feet of straight duct. For example two 3 foot straight sections connected by a 90ÃÂº elbo might be equivalent to 10 feet of straight pipe. So you'll need to figure the equivalent straight line duct length then size it's diameter to reduce resistance. The instructions with the hood should provide enough info for you to figure it out. A 6 inch dia pipe has 44% more area than a 5 inch dia pipe. 5 inch is pretty much standard so watch it. If the pipe is too small the hood won't work for diddly. Don't count on the contractor to be able to handle that horribly advanced mathematical concept. Don't. We have a downdraft type cook top with 5 inch pipe. I shoulda been 6 inch. Total length is about 15 feet but the equivalent straight length is roughly 25 feet. It runs thru the crawl space and xosts to the outside. Most grease stops in a trap but the fan and housing collect a lot over the years. Not much if any goes into the pipe. It's a centrifugal fan so the grease gets thrown to the housing instead of being impelled along the duct. If your fan is not centrifugal that may not be true.
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Nadine--I think those slide out hoods are going to require a lot of the space in the cabinet above so you're going to lose that space anyway. So you might want to consider a more conventional undercabinet hood, too. Depending on your situation, you may be able to vent directly out the back of hood into your existing vent and not lose any of the cabinet space. It won't be quite as accessible though as you realize. I'm assuming that your rectangular vent is 3.25 x 10" which is roughly equivalent to a six inch round duct. So you need to look at hoods with CFM's sized for that size of duct. Unless you know exactly how your vent is situated, you need to remove the microwave. A lot of hoods will be adaptable to horizontal rectangular, vertical rectangular vent and vertical round exhaust. I know that my Zephyr hood had all three options. Zephyr Typhoon I disagree that you will get 'tremendous' noise. Not going to be whisper quiet but will most likely be substantially less noisy than most micro hoods. Here is a link that might be useful: Slide out range hood
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For the wall vent option, also consider the proximity of operable windows. Codes vary by locality, so you should probably call you local building inspector for clarification, but in my city in Northern California the vent must be >=3' from any operable windows. Folks above are correct that 90s in ducts result in pressure drop, but you're talking about a short run with a single bend, and you could always run a slightly larger duct if you were concerned about it, so I don't think the pressure drop from the single turn is a significant consideration because it's gonna work well either way. Primary considerations are: cost to install, how it looks, if smoke will find it's way back into house or otherwise annoy outside.
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Lisa Leone
Original Author
2 months ago
@kaseki I was basing it off the range size (30"x24" and 90 cfm/sqft) and the max output of the burners (online calculator, 42.1k BTU for all burners together), giving me a needed CFM between 320 and 450. I was going to get a 36" wide hood to give 3" extra on each side. There is plenty of room around the duct to have extra space, so a silencer would be really interesting.

I have read that under 400 cfm doesn't need make-up air, and additionally I live in a very old and drafty house, BUT we do have an oil boiler furnace for hydrostatic radiators in the basement that has an open chimney, so should I install make up air? Could it be some kind of passive system, like a vent with a damper that goes to our somewhat heated but separate (not over basement mud room?

Thank you so much for your help!

These are some of the hoods I was considering:

whirlpool

https://www.build.com/whirlpool-wvw53uc6h/s1512649?uid=3547708&searchId=yFvl0spnaE

broan

https://www.build.com/broan-ew4836/s1718763?uid=4061054&searchId=wPjFuAkFWM

Kobe

https://www.build.com/product/s877100?uid=2235490

Kobe

https://www.build.com/kobe-chx2236sqb-wm-1/s1189295?uid=2849905&searchId=8WjkjWgOLJ

Zephyr

https://www.build.com/zephyr-zsi-e36a-es/s1115832?uid=2675796&searchId=oVg69NRkkV
kaseki
2 months ago
If you are going to do searing or wok type cooking, then the 90 CFM/sq.ft. value is what you want. But that is for actual flow. Multiply by 1.5 for the blower rating. E.g., 600 - 700 CFM for the 30-inch hood, proportionately larger for the 36-inch hood. If no hot oil cooking, then you could get by with using 60 CFM/sq. ft., and some of the lower rated hoods listed above might be suitable. Just keep in mind that whatever CFM they tout, the actual flow is likely to not exceed 2/3 of that value.

I know that Beckett and likely the other burner manufacturers have MUA kits, and I would suggest they be used even without kitchen ventilation issues.

However, you still need a source of air for the hood. This may be accomplished in many ways, but you have noted one of the easier ones; dump air into a mud room and heat it in the room. You may need more heat than you have now, but this can be provided by many different schemes and can just operate to keep the room at some temperature and not be linked into the hood controls.

If the mud room has hydronic heating, either supplement it with electric heating, or be sure it is on its own zone and has enough heating capacity. (see chart)

In considering hood designs (and I'm not going to rate those listed above), keep in mind that if you use a silencer (12 inches diameter on an 8-inch duct; 10-inches on 6-inch duct), the top of the hood has to be compatible with whatever enclosure you intend to use over the silencer. You may have to use a local sheet metal shop to fabricate what you need.

The silencer requires the blower be downstream. Here is an image of a Broan blower that would typically be used on a sloped roof, but should be fine on an exterior wall. Wolf uses Broan for blower manufacture, I believe, so their external blowers should look similar. Abbaka (now part of Bluestar) also make such blowers.

With an external blower, you can choose your hood for size and shape, and not care what blowers they might have squeezed in. Fan motor control compatibility needs to be checked.
Lisa Leone thanked kaseki

Should range hood exhaust go horizontal or up then out?

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Lisa Leone
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Should range hood exhaust go horizontal or up then out?

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Lisa LeoneOriginal Author

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kaseki

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Lisa Leone
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